Glaucoma is the leading cause of irreversible blindness worldwide. It is a retinal neurodegenerative disorder where retinal ganglion cells (RGC) and their axons (that form the optic nerve) are lost. Even though elevated intraocular pressure is a known risk factor and an observed symptom for the disease, such pressure measurements are not reliable for diagnosing glaucoma. Current psychophysical methods used in clinical practice for detecting glaucoma depend on the occurrence of significant progressive loss of axons with approximately 40% of optic nerve axons needing to be lost before a functional change in peripheral vision can be clinically detected. Clearly, these current methods cannot detect the early onset of the disease as they depend on the patient's ability and cooperation to identify the areas of functional defects in the field of vision. Additional methods to detect and diagnose glaucoma are desired. Several objective imaging techniques have been developed in an attempt to address this need.
Scanning laser polarimetry (SLP), confocal scanning laser ophthalmoscopy (CSLO) and optical coherence tomography (OCT) are used for this purpose. They either measure the charges that occur in the optic nerve head or the thickness of the retinal nerve fiber layer (RNFL). Methods that image/measure the retinal nerve fiber layer utilize birefringence/interferometric based methods and are hindered by the limitations of such methods including phrase wrapping artifacts and poor signal-to-noise ratio. Additionally, the disease must progress to the point where a morphological change in the retinal nerve fiber layer can be detected. An alternative technique for the early detection of glaucoma is therefore desired that addresses at least some of these shortcomings.